Fixed Reader.cardDetectTask cancellation in the StopCardEvents().

[tsvx]

It had hung while in the Visual Studio debugger.

[tsvx]

The issue had occured while running ReadTestApp in the Visual Studio 2015 using F5 key. After I pressed any key to stop the app, it had hung. One thread had been spinning in the do { ... } while (true); loop of the StopCardEvents() and another had been hung on the last line of the RunCardDetectionEx(): cancellationToken.ThrowIfCancellationRequested();. The latter is absolutely unclear for me though.

This issue doesn't appear when running the app without debugging.